Chain alignment structure of bicycle transmission

ABSTRACT

The present invention provides a chain alignment mechanism of a transmission for a bicycle which includes a drive sprocket wheel which is rotatably driven by a crankshaft, a driven sprocket wheel which is drivably connected with an output shaft which is rotated in an interlocking manner with a drive wheel of the bicycle, and an endless chain which is wound around the above-mentioned drive sprocket wheel and the above-mentioned driven sprocket wheel, wherein even when the chain of the transmission for the bicycle is deflected or slackened due to a driving manipulation of the bicycle, the vertical vibration of the bicycle or the like, the chain is reeled in the drive sprocket wheel in a row in an aligning manner. A chain guide member is arranged on an endless-chain-reel-in side of the above-mentioned drive sprocket wheel.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 USC 119 to JapanesePatent Application No. 2004-034265 filed on Feb. 10, 2004 the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a chain alignment structure of atransmission for a bicycle.

2. Description of Related Art

A transmission for a bicycle according to the present invention relatesto a chain alignment structure of a bicycle transmission which includesa drive sprocket wheel which is rotatably driven by a crankshaft, adriven sprocket wheel which is drivably connected with an output shaftwhich is rotated in an interlocking manner with a drive wheel (usually arear wheel) of a bicycle, and an endless chain which is wound around thedrive sprocket wheel and the driven sprocket wheel. In the related art,the chain alignment structure of a transmission having such aconstruction is not known. In view of this, related art from a similartechnical field will be discussed.

Conventionally, the deflection of a chain attributed to the transmissionor the vibration which is generated between a reel-in side of the drivesprocket wheel and a reel-out side of the driven sprocket wheel isreceived such that the chain 8 is received from below by a chainreceiving portion 12 which is formed on an upper portion of a pulley arm9 which is fixed to a chain stay 2′ (numerals being numerals describedin following cited document). However, since the chain receiving portionis arranged only below the chain, although the downward deflection ofthe chain is restricted, the chain receiving portion does not serve torestrict the upward movement of the chain (for example, seeJP-UM-55-1551).

SUMMARY AND OBJECTS OF THE INVENTION

It is an object of the present invention to provide a chain alignmentstructure that allows a chain of a transmission of a bicycle to bereeled in a drive sprocket wheel in an aligned manner in a row even whenthe chain is deflected or slackened due to a driving manipulation,vertical vibration or the like of the bicycle.

The present invention has been made to overcome the above-mentionedtask. According to a first aspect of the present invention, a chainalignment structure of a bicycle transmission includes a drive sprocketwheel which is rotatably driven by a crankshaft, a driven sprocket wheelwhich is drivably connected with an output shaft which is rotated in aninterlocking manner with a drive wheel of a bicycle, and a chain whichis wound around the drive sprocket wheel and the driven sprocket wheel,wherein a chain guide member is arranged on an endless-chain-reel-inside of the drive sprocket wheel.

According to a second aspect of the present invention, the drivensprocket wheel is configured to be always integrally rotated with theoutput shaft, and a one-way clutch, which transmits the rotation in thenormal direction of the crankshaft to the drive sprocket wheel, isarranged between the crankshaft and the drive sprocket wheel.

According to a third aspect of the present invention, the chain guidemember includes a pair of guide portions which are arrangedsubstantially in parallel with a transmission locus of the chain in astate that the guide portions sandwich the chain, and the pair of guideportions are connected with each other by way of a connecting portion.

According to a fourth aspect of the present invention, the drivensprocket wheel and the drive sprocket wheel are covered with a singlecasing which is fixed to the vicinity of the crankshaft, and the chainguide member is fixed in the inside of the casing.

According to a fifth aspect of the present invention, the plurality ofdriven sprocket wheels which differ in diameter are coaxially mounted onthe output shaft, a winding changeover unit which changes over thewinding among the plurality of driven sprocket wheels around which theendless chain is wound is provided, and the chain guide member allowsthe movement of the endless chain in the axial direction of the drivensprocket wheel.

According to a sixth aspect of the present invention, rollers arearranged in the chain guide member.

According to a seventh aspect of the present invention, the rollers arearranged outside an annular space that the endless chain defines.

Due to the first aspect of the present invention, it is possible torestrict the upward and downward deflection of the chain at the endlesschain reel-in side of the driven sprocket wheel and hence, it ispossible to feed the aligned chain to the drive sprocket wheel.Accordingly, the smooth movement of the endless chain can be realized.

Due to the second aspect of the present invention, when the chain isrotatably driven based on an input from the rear wheel, the slackeningof the chain which is generated between the reel-out side of the drivensprocket wheel and the reel-in side of the drive sprocket wheel can beeliminated and hence, the chain can be aligned.

Due to the third aspect of the present invention, it is possible toefficiently perform the alignment of the chain while ensuring spacesaving.

Due to the fourth aspect of the present invention, it is possible tosupport the chain guide member on the casing having the high supportingrigidity.

Due to the fifth aspect of the present invention, it is possible tomaintain the alignment function even when the winding of the endlesschain is changed over.

Due to the sixth aspect of the present invention, it is possible toalign the chain further smoothly.

Due to the seventh aspect of the present invention, it is possible toalways bring the rollers into contact with the chain.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 is a schematic left side view of a bicycle according to oneembodiment of the present invention;

FIG. 2 is a left side view of a left casing;

FIG. 3 is a right side view of a right casing;

FIG. 4 is a right side view which allows the observation of the insideof a transmission T by removing a part of a right cover of thetransmission T;

FIG. 5 is a cross-sectional view taken along a line V-V in FIG. 4;

FIG. 6 is a cross-sectional view taken along a line VI-VI in FIG. 4;

FIG. 7 is a cross-sectional view taken along a line VII-VII in FIG. 6;

FIG. 8 is a cross-sectional view taken along a line VIII-VIII in FIG. 4;

FIG. 9 is an enlarged partial cross-sectional view of an essential partof a derailleur;

FIG. 10 is a cross-sectional view taken along a line X-X in FIG. 9;

FIG. 11 is an view as viewed in an arrow XI direction in FIG. 8 showinga mounting state of a wire guide member;

FIG. 12 is a cross-sectional view taken along a line XII-XII in FIG. 4;

FIG. 13 is a cross-sectional view taken along a line XIII-XIII in FIG. 4in another state;

FIG. 14 is a cross-sectional view taken along a line XIV-XIV in FIG. 4;

FIG. 15 is a right side view of the above-mentioned second derailleurarm 84;

FIG. 16 is a cross-sectional view taken along a line XVI-XVI in FIG. 15;

FIG. 17 is a right side view of the above-mentioned drive sprocket wheelmovement restricting member 121;

FIG. 18 is a cross-sectional view taken along a line XVIII-XVIII in FIG.17;

FIG. 19 is a right side view showing only members relevant to thetransmission chain alignment in the inside of a transmission casing;

FIG. 20 is a side view of the above-mentioned chain guide member 130.

FIG. 21 is a top plan view of the chain guide member 130;

FIG. 22 is a right side view showing only members relevant to thetransmission chain alignment in the inside of the casing with respect toanother embodiment of the chain guide member;

FIG. 23 is a side view of the above-mentioned chain guide member;

FIG. 24 is a cross-sectional view taken along a line XXIV-XXIV in FIG.23;

FIG. 25 is a cross-sectional view taken along a line XXV-XXV in FIG. 23;and

FIG. 26 is a cross-sectional view taken along a line XXVI-XXVI in FIG.23.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of a transmission according to the present inventionillustrated in FIG. 1 to FIG. 21 will be hereinafter explained.

FIG. 1 is a left side view of a bicycle B in which the transmissionaccording to the present invention is used. The bicycle is a downhillbicycle and is used in a competition wherein players compete againsttime for descending an unpaved course which includes high-speed cornersand jump sections in a woodland path or the like.

A vehicle body frame F of the bicycle B includes a pair of left andright main frames 2 which extend rearwardly, obliquely and downwardlyfrom a head pipe 1, a down tube 3 which extends rearwardly, obliquelyand downwardly from front end portions of both main frames 2 below thefront end portions, and a saddle frame 4 which extends rearwardly fromcenter portions of respective main frames 2.

The saddle frame 4, which supports a saddle 6, is supported on a stay 4a, which is interposed between the saddle frame 4 and the main frames 2.

The head pipe 1 steerably supports a pair of left and right front forks5 and a front wheel Wf is pivotally supported on lower end portions ofthe front forks 5.

Hereinafter, “up-and-down”, “front-and-rear” and “left-and-right” aredetermined using the bicycle as the reference with respect to“up-and-down,” “front-and-rear” and “left-and-right” of the bicycle.Further, the side viewing implies the viewing in the left-and-rightdirection.

On a pivot shaft 7 which is provided to a rear portion of the left andright main frames 2 illustrated in FIG. 1, as shown in FIG. 5, front endportions of a pair of left and right swing arms 8 are tiltably andpivotally supported in a state wherein the swing arms 8 are arrangedclose to respective inner side surfaces of the pair of left and rightmain frames 2. On rear end portions of the swing arms 8, a rear wheel Wrthat is positioned between the pair of left and right main frames 8 ispivotally supported by way of an axle 9.

The pair of left and right swing arms 8 are, as shown in FIG. 1,connected with the pair of left and right main frames 2 by way of asuspension 10 which has a compression spring and a damper, the pair ofleft and right swing arms 8 are tiltable in the up-and-down directionabout the pivot shaft 7.

A power transmission unit that includes a crankshaft 11, a transmissionT and a drive force transmission mechanism, which transmits a drive,force to the rear wheel Wr is provided on the bicycle B.

As shown in FIG. 1, below the vehicle body frame F and between rearportions of both main frames 2 and the rear portion of the down tube 3,a crankshaft 11 and the transmission T are arranged. On a right side ofthe bicycle B, a mechanism which transmits the drive force from thetransmission T to the rear wheel Wr, that is, the drive forcetransmission mechanism which includes a rear wheel drive sprocket wheel15, a rear wheel driven sprocket wheel 16 and an endless rear wheeldrive chain 17 which extend between and are wound around both sprocketwheels, is arranged on a right side of a vehicle-body-width-directioncenter line.

A casing 20 of the transmission T, as shown in FIG. 2, FIG. 3 and FIG.5, includes a left casing 20L and a right casing 20R which are dividedor split in the left-and-right direction and are merged together. Outerside views of the left and right casings 20L, 20R are illustrated inFIG. 2 and FIG. 3.

The left and right casings 20L, 20R include a left cover 21L and a rightcover 21R made of CFRP (carbon fiber reinforced plastic) whichrespectively incorporate inner units therein and a left reinforcingmember 22L and a right reinforcing member 22R which reinforce the leftand right covers 21L, 21R from the outside. Here, the left cover 21L isadhered to the inside of the left reinforcing member 22L and the rightcover 21R is adhered to the inside of the right reinforcing member 22R.

The left and right covers 21L, 21R, as shown in FIG. 8, abut relative toeach other with a sealing member 31 inserted between mating surfacesthereof and are fastened and are integrally formed by bolts 32, 33 whichare inserted into bolt holes 23L, 23R, 24L, 24R formed in outerperipheral projecting portions of the left and right reinforcing members22L, 22R which sandwich the left and right covers 21L, 21R.

Also shown in FIG. 1 along with FIG. 2 and FIG. 3, by inserting thebolts 32 into three bolt holes 23L, 23R provided to each one of the leftand right sides, the left and right reinforcing members 22L, 22R aremerged and fastened together. On the other hand, out of another threebolt holes 24L, 24R provided to each one of left and right sides, twofront bolt holes 24L, 24R are fastened together to a lower end of thedown tube 3 by inserting the bolts 33 and one rear bolt hole 24L, 24R isfastened together to lower ends of the main frames 2 by inserting abolt.

That is, the bolt holes 24L, 24R have not only the function of fasteningthe left and right casings 20L, 20R by inserting the bolts 33 but alsothe function of mounting the transmission T to the main frames 2 and thedown tube 3 of the vehicle.

In lower portions of the left and right reinforcing members 22L, 22R ofthe casing 20, as shown in FIG. 5, crankshaft receiving holes 25L, 25Rare formed with the crankshaft 11 penetrating the crankshaft receivingholes 25L, 25R in the left-and-right direction. In addition, pivotbearing holes 26L, 26R are provided which allow the pivot shaft 7 topenetrate therethrough. The pivot bearing holes 26L, 26R are formedabove the crankshaft receiving holes 25L, 25R.

Further, as shown in FIG. 2, with respect to the left reinforcing member22L, a derailleur bearing hole 27L for a derailleur shaft 81 which willbe describe later and a peeping hole 28L which is spaced apart from thebearing hole 27L are formed in an upper portion thereof. On the otherhand, as shown in FIG. 3, with respect to the right reinforcing member22R, a derailleur bearing hole 27R which faces the derailleur bearinghole 27L in an opposed manner and a peeping hole 28R which is spacedapart from the derailleur bearing hole 27L are formed in an upperportion thereof. Further, an output bearing hole 29 is formed in a frontportion of the right reinforcing member 22R.

Here, the left and right peeping holes 28L, 28R are not arranged atpositions where the left and right peeping holes 28L, 28R face eachother in an opposed manner but are arranged at given rotational angularpositions about the derailleur bearing holes 27L, 27R. An inner diameterof the left and right peeping holes 28L, 28R is slightly larger than adiameter of guide pulley support shafts 87 to facilitate the viewing ofthe guide pulley support shafts 87, and is largely smaller than an outerdiameter of the guide pulleys 86. This is because that by preventing theinner diameter of the left and right peeping holes 28L, 28R from beingexcessively enlarged, the rigidity of the casing 20 can be ensured.

Further, as shown in FIG. 3, a stopper bolt hole 30 is formed in thevicinity of the derailleur bearing hole 27R of the right reinforcingmember 22R.

The above-mentioned left and right reinforcing members 22L, 22R aremerged with the left and right covers 21L, 21R and, thereafter, arefastened by the bolts 32, 33 thus constituting the casing 20 of thetransmission T. The transmission T is suspended from the vehicle bodyframe F.

As shown in FIG. 5, the crankshaft 11 which constitutes a pedal-typecrankshaft is provided in a state wherein the crankshaft 11 penetratesthe left and right crank bearing holes 25L, 25R of the casing 20 and hasleft and right end portions thereof projecting outside the casing 20. Apair of crank arms 12 has proximal ends thereof fitted on the projectingleft and right end portions of the crankshaft 11. As shown in thedrawings, pedals 39 are rotatably mounted on distal ends of the crankarms 12.

As shown in FIG. 1 and FIG. 5, the bolt-like pivot shaft 7 extends bypenetrating a through hole 2 c of a pivot boss 2 b which is formed on arear portion 2 a of the main frame 2 and bushings 13 which are fitted inpivot bearing holes 26L, 26R formed in the left and right reinforcingmembers 22L, 22R of the casing 20, and is fixed to a rear portion of themain frame 2 by a nut 34 which is threadedly engaged with a distal endof the bolt-like pivot shaft 7. The respective swing arms 8 are tiltablysupported on the pivot shaft 7 on the left and right outsides of thecasing 20 and between the casing 20 and the rear portions of therespective main frames 2 by way of a collar 18 and a bearing 19.

FIG. 4 is a right side view of the inside of the transmission T with aportion of the right casing 20R taken away. FIG. 6 is a cross-sectionaldeveloped view taken along a line VI-VI in FIG. 4 that illustrates aportion that is relevant to the crankshaft 11 and the output shaft 14.

On a right end portion of the output shaft 14 which is accommodated inthe inside of the casing 20 and projecting outwardly from an outputbearing hole 29 of the right casing 20R, the rear-wheel drive sprocketwheel 15 is fitted on.

As shown in FIG. 1, a rear wheel drive chain 17 extends between and iswound around the rear-wheel drive sprocket wheel 15 and the rear-wheeldriven sprocket wheel 16 which is formed on the rear wheel Wr.

The rear-wheel drive sprocket wheel 15, the rear-wheel driven sprocketwheel 16 and the rear wheel drive chain 17 constitute the drive forcetransmission mechanism which drives the rear wheel Wr which is a drivewheel of the vehicle.

The output shaft 14 is always operated in an interlocking manner withthe rear wheel Wr and is rotated in the forward direction P and thebackward direction Q in an interlocking manner with the rear wheel Wr.

FIG. 8 is a cross-sectional developed view taken along a line VIII-VIIIin FIG. 3 that illustrates portions relevant to the guide pulley supportshaft 87 and the derailleur shaft 81.

In FIGS. 4, 5, 6 and 8, the transmission T includes a transmissionmechanism M1 and a transmission changeover mechanism M2 that areaccommodated in the inside of the casing 20.

The transmission mechanism M1 mainly includes portions that are relevantto the crankshaft 11 and the output shaft 14 shown in FIG. 5 and FIG. 6,while the transmission changeover mechanism M2 mainly includes portionsthat are relevant to the derailleur shaft 81 shown in an upper portionof FIG. 8.

The transmission changeover mechanism M2 acts on the transmissionmechanism M1 to perform the shifting to move the transmission mechanismM1 to a desired transmission position.

The transmission mechanism M1 includes the one-way clutch 42 shown inFIG. 7, a slide mechanism S, a drive sprocket wheel body 40, atransmission sprocket wheel body 50, an endless transmission chain 58and the output shaft 14 shown in FIG. 6.

The transmission sprocket wheel body 50 includes a plurality of sprocketwheels 51 to 57 connected to the output shaft 14 in an overlapped mannerin multiple stages with a gap therebetween in an ascending order fromthe left side to the right side.

As shown in FIG. 5, the crankshaft 11 is rotatably supported on thecasing 20 by way of the pair of right and left bearings 48 which arefitted in the crankshaft holes 25L, 25R of the left and rightreinforcing members 22L, 22R of the casing 20. The crank arms 12 areintegrally fitted on both ends of the crankshaft 11. As shown in FIG. 1,the pedals 39 are pivotally mounted on the distal ends of the crank arms12. The utilizing the legs of a rider, not shown in the drawing, whosits on the saddle 6 in a striding manner, the crankshaft 11 isrotatably driven in the advancing direction P.

In FIG. 6, with respect to the crankshaft 11, the drive sprocket wheelbody 40 is arranged between both the bearings 48 and the drive sprocketwheel 41 of the drive sprocket wheel body 40 and is mounted on thecrankshaft 11 by way of the one-way clutch 42 and the slide mechanism Swhich are coaxially arranged with the crankshaft 11. The drive sprocketwheel body 40 is rotatably driven by the crankshaft 11.

As shown in FIGS. 6 and 7, the one-way clutch 42 includes a clutch innerrace 42 a which is constituted of an outer peripheral portion per sewhich is a portion of the crankshaft 11, a clutch outer race 42 b whichis constituted of a portion of an inner cylinder 44 described later, aplurality of ratchet pawls 42 c which are engaged with engaging portionsformed on an inner periphery of the clutch outer race 42 b, and a ringspring 42 d which is mounted on the clutch inner race 42 a and biasesthe ratchet pawls 42 c such that distal ends of the ratchet pawls 42 care engaged with recessed portions formed in an inner peripheral surfaceof the clutch outer race 42.

Due to an action of the one-way clutch 42, only when the rider steps onthe pedals 39 so as to rotate the crankshaft 11 in the advancingdirection P which advances the vehicle, the rotational force of thecrankshaft 11 is transmitted to the drive sprocket wheel 41. Further,during the advancing of the vehicle, when the rider stops stepping onthe pedals 38 and the drive sprocket wheel 41 is rotated in theadvancing direction P, that is, the crankshaft 11 is rotated in theretracting direction Q relatively with respect to the drive sprocketwheel 41, the transmission of the rotational force from the drivesprocket wheel 41 to the crankshaft 11 is interrupted.

In FIG. 6, between the one-way clutch 42 and the drive sprocket wheel41, the slide mechanism S is provided, wherein the slide mechanism Sallows the drive sprocket wheel 41 to move in the crankshaft axialdirection with respect to the crankshaft 11 and, at the same time,allows the drive sprocket wheel 41 to be rotated integrally with theclutch outer 42 b of the one-way clutch 42.

The slide mechanism S includes an inner sleeve 44, an outer sleeve 45and a ball spline mechanism 46.

The inner sleeve 44 is a sleeve, which constitutes the above-mentionedclutch outer 42 b with a right end thereof and is rotatably supported onan outer periphery of the crankshaft 11 by way of a pair of needlebearings 43, while the outer sleeve 45 is a sleeve, which is arrangedradially outside the inner sleeve 44.

The ball spline mechanism 46 is a spline engagement mechanism which usesballs between an outer peripheral surface of the inner sleeve 44 and aninner peripheral surface of the outer sleeve 45. The drive sprocketwheel 41 and a drive sprocket wheel movement restricting member 121 areintegrally connected to the outer sleeve 45 by rivets 125 which arecaulked after penetrating respective rivet holes 122, 123, 124 formed inthe outer sleeve 45, the drive sprocket wheel 41, and the drive sprocketmovement restricting member 121. Accordingly, the outer sleeve 45, thedrive sprocket wheel 41 and the drive sprocket wheel movementrestricting member 121 are integrally moved along the crankshaft 11 and,at the same time, are rotated with respect to the casing 2.

A chain guide 47 is integrally mounted on the outer peripheral portionof the drive sprocket wheel 41 by rivets 49.

As shown in FIGS. 5 and 6, the ball spline mechanism 46 which integrallyrotates the slide mechanism S and the drive sprocket wheel 41 and, atthe same time, allows the drive sprocket wheel 41 and the outer sleeve45 to move in the crankshaft axial direction with respect to the innersleeve 44 includes a plurality of pairs of accommodating grooves 46 a,46 b having a semicircular cross section which are formed of an outerperipheral surface of the inner sleeve 44 and the inner peripheralsurface of the outer sleeve 45, face each other in an opposed manner inthe radial direction and are directed in the crankshaft direction. Rowsof balls include a plurality of balls 46 c which are accommodatedrotatably in respective pairs of accommodating grooves in a stridingmanner, and engage with the inner sleeve 44 and the outer sleeve 45 inthe circumferential direction. To restrict the movable range of thedrive sprocket wheel 41 and the outer sleeve 45 and, at the same time,to prevent the removal of the balls 46 c, stoppers 44 a, 44 b, 45 a, 45b are provided to both end portions of the inner sleeve 44 and the outersleeve 45.

As shown in FIGS. 6, 12 and 13, the output shaft 14 is rotatablysupported by way of the pair of left and right bearings 48 which arerespectively held by the left and right reinforcing members 22L, 22R ofthe casing 20.

Between the left and right bearings 48 for the output shaft 14, themulti-stage transmission sprocket wheel body 50 for the transmissionincludes the plurality of transmission sprocket wheels that are mountedon the output shaft 14 such that the transmission sprocket wheel body 50is constantly integrally rotated with the output shaft 14. In thisembodiment, the above-mentioned multi-stage transmission sprocket wheelbody 50 is a sprocket wheel body which includes transmission sprocketwheels 51 to 57 for seven types of transmission which differ in outerdiameter relative to each other.

Seven transmission sprocket wheels 51 to 57 are arranged in the outputshaft axial direction such that the speed is sequentially lowered fromthe right side to the left side from the transmission sprocket wheel 57for the seventh speed (maximum speed) having the minimum outer diameterto the transmission sprocket wheel 51 for the first speed (the minimumspeed) having the largest outer diameter and, at the same time, thetransmission sprocket wheel 51 to 57 are connected to the output shaft14 in a spline engagement on the outer peripheral surface of the outputshaft 14.

The transmission chain 58 extends between and is wounded around thedrive sprocket wheel body 40 and the transmission sprocket wheel body 50so as to transmit the rotation between the crankshaft 11 and the outputshaft 14 by means of the transmission chain 58.

The transmission changeover mechanism M2 described later is a mechanismwhich performs the transmission by changing over the winding of thetransmission chain 58 among the group of transmission sprocket wheels 51to 57. That is, the transmission changeover mechanism M2 functions toextend the transmission chain 58 between one transmission sprocket wheelwhich is selected out of the transmission sprocket wheels 51 to 57 bythe transmission changeover mechanism M2 and the above-mentioned drivesprocket wheel 41.

Accordingly, the output shaft 14 is rotatably driven by the crankshaft11 with a transmission ratio which is determined by a tooth number ratiobetween the above-mentioned transmission sprocket wheels 51 to 57 andthe drive sprocket wheel 41.

Then, the power of the output shaft 14 is transmitted to the rear wheelWr by way of the rear wheel drive sprocket wheel 15, the rear wheeldrive chain 17 and the rear wheel driven sprocket wheel 16 (see FIG. 1)which are provided on the right side and outside of the casing 20.

FIG. 8 is a cross-sectional view taken along a line VIII-VIII in FIG. 3and shows portions which are mainly relevant to the derailleur shaft 81of the transmission mechanism M2. FIG. 12 is a cross-sectional developedview taken along a line XII-XII in FIG. 3 and is a cross-sectionaldeveloped view which is formed by adding a cross-sectional view of theoutput shaft 14 to the above-mentioned cross-sectional view. FIG. 13shows another state.

In FIGS. 1, 8 and 12, the transmission changeover mechanism M2 which isoperated by a transmission manipulating mechanism 60 includes thederailleur 80 which has the guide pulley 86, and a tensioner 100 whichhas a tensioner pulley 105.

Further, as shown in FIG. 4, the transmission chain 58 is wound aroundthe drive sprocket wheel 41 and the above-mentioned transmissionsprocket wheels 51 to 57. Further, during operation, the transmissionchain 58 is wound around the guide pulley 86 and the tensioner pulley105 which are arranged at a side where the transmission chain 58 isslackened.

The transmission manipulating mechanism 60 shown in FIG. 1 includes atransmission manipulating member 61 which includes a transmission leveror the like which is manipulated by the rider, a wire 62 which connectsthe transmission manipulating member 61 and the derailleur 80 totransmit an operation of the transmission manipulating member 61 to thederailleur 80, and an outer tube 63 which covers the wire 62. See FIG. 1and FIG. 8.

In FIG. 8, the derailleur 80 includes a derailleur shaft 81 which isrotatably supported on an upper front portion of the casing 20, aderailleur arm 82 which has a proximal end portion thereof slidablyfitted on and supported on the derailleur shaft 81 in a state that theproximal end portion is turnable and movable in the axial direction, aguide pulley 86 which is rotatably supported on a distal end portion ofthe derailleur arm 82, a compression coil spring 91 which pushes thederailleur arm 82 along the derailleur shaft 81 in the rightwarddirection, a manipulating pin 65 which constitutes a manipulatingelement for moving the derailleur arm 82 with respect to the derailleurshaft 81 in response to the transmission manipulation by thetransmission manipulating mechanism 60, and a balancing spring 92 whichis constituted of a torsional coil spring which biases the derailleurarm 82 in the rotating direction (see FIG. 4) which is directed to theoutput shaft 14 against a tension of the transmission chain 58 which isapplied by the tensioner pulley 105.

As shown in FIGS. 5, 12 and 13, the derailleur shaft 81 is rotatablysupported on the casing 20 such that a center line thereof becomesparallel to a rotation center line of the transmission sprocket wheelbody 50, while the guide pulley 86 is supported on the derailleur arm 82such that a rotation center line thereof becomes parallel to therotation center line of the transmission sprocket wheel body 50.

More particularly as shown in FIG. 8, a left end portion of thederailleur shaft 81 is rotatably supported on the left reinforcingmember 22L by way of the bearing cap 68 which is fitted in thederailleur bearing hole 27L of the left reinforcing member 22L, while aright end portion of the derailleur shaft 81 is rotatably supported onthe right reinforcing member 22R in a state wherein the right endportion is fitted in the derailleur bearing hole 27R of the rightreinforcing member 22R.

Here, an opening of the derailleur bearing hole 27R of the rightreinforcing member 22R is closed by inserting the cap 69 therein fromthe outside.

The bearing cap 68 is positioned and mounted such that the bearing cap68 is inserted in the derailleur bearing hole 27L of the leftreinforcing member 22L from the inside, the flange portion 68 a isfitted in an inner shoulder portion of the derailleur bearing hole 27L,and a retainer ring 98 is fitted in an annular groove formed in an outerperipheral surface of the left end of the bearing cap 68. The derailleurshaft 81 which penetrates the bearing cap 68 and is rotatably supportedby the bearing cap 68 has its movement thereof in the right directionrestricted such that a retainer ring 95 which is fitted in an annulargroove formed in the outer peripheral surface is brought into contactwith a washer 94 which is fitted on an outer peripheral surface of aprojecting end portion of the derailleur shaft 81. The leftward movementin the axial direction of the derailleur shaft 81 is restricted by awasher 93 which is fitted on a shoulder portion formed on an outerperipheral surface in the inside of the derailleur shaft 81.

Accordingly, although the rotation of the derailleur shaft 81 isallowed, the movement of the derailleur shaft 81 in the axial directionis restricted.

As shown in FIG. 8, the balancing spring 92 which is wound around theouter periphery of the derailleur shaft 81 has a right end 92 a whichconstitutes one end thereof engaged with a portion of the derailleurshaft 81 at a position along the washer 93 and a left end 92 b whichconstitutes another end engaged with the bearing cap 68.

That is, between the bearing cap 68 and the derailleur shaft 81, thebalancing spring 92 which is constituted of a torsional coil spring isinterposed in the relative rotational direction.

As shown in FIGS. 8 and 9, a pair of twisted guide holes 81 a, 81 awhich are gently spirally inclined in the axial direction are formed ina sleeve wall of the cylindrical derailleur shaft 81 in a center axissymmetry. As shown in FIG. 10, a pair of rollers 66, 66 which arearranged on the manipulating pins 65 which penetrate both guide grooves81 a, 81 a are respectively fitted in the guide holes 81 a, 81 a in arotatable manner.

As shown in FIGS. 9 and 10, a ring-like roller 66 having an outerdiameter of 6 mm and an inner diameter of 3 mm is rotatably pivoted onthe manipulating pin 65 having a diameter of 3 mm. The roller 66 isfitted in a guide hole 81 a having a width of 6 mm or more such that theroller 66 is rotatable in the inside of the guide hole 81 a.

Although a twisting angle of the guide hole 81 a, an inclination anglewith respect to a mother line which is parallel to the center axis lineof the derailleur shaft 81, is approximately 40 degree, when themanipulating pin 65 moves in the inside of the guide hole 81 a, themanipulating pin 65 and the roller 66 function to rotate the derailleurshaft 81 and the rotating force twists the balancing spring 92 byapproximately 10 degree so that the manipulating pin 65 which isindirectly fitted in the guide hole 81 a by way of the roller 66 isturnable together with the derailleur arm 82 within a range of 30°.

As shown in FIG. 10, the manipulating pin 65 extends further outsidethan both rollers 66, 66 and has both ends thereof fitted on proximalend portions 84a of the second derailleur arm 84 in the derailleur arm82 which penetrates the derailleur arm 81 and is pivotally supported ina state that the derailleur arm 82 is turnable and movable in the axialdirection.

A connecting hook 67 is mounted on a center portion of the manipulatingpin 65 which is positioned at an intermediate position between both ofthese rollers 66, 66 by way of an engagement of a U-shaped end portion.

A wire 62 is inserted into the inside of the derailleur shaft 81 througha small hole formed on a center line of the derailleur shaft 81 at thecenter of the guide cap 64 which covers a left-end opening of thederailleur shaft 81, and a distal end of the wire 62 is connected to oneend of the connecting hook 67.

perform the assembling steps for connecting the wire 62 to themanipulating pin 65 is, as shown in FIG. 8, the wire 62 is inserted intothe inside of the derailleur shaft 81 through the small hole formed inthe center of the guide cap 64, the wire 62 is made to pass through thecenter portion, between the rollers 66, 66, of the manipulating pin 65and to project from the opening of the derailleur bearing hole 27R, andthe connecting hook 67 is connected to the distal end of the wire 62.

Then, the wire 62 is pulled leftward by grasping a portion of the wire62 which is extended from the guide cap 64 so as to pull the connectinghook 67 connected to the wire 62 into the inside of the derailleur shaft81, and the U-shaped end portion of the connecting hook 67 is engagedwith the center portion of the manipulating pin 65 thus achieving theabove-mentioned assembled means.

Here, after assembling, the cap 69 is fitted into the opening of thederailleur bearing hole 27R of the right reinforcing member 22R so as toplug the opening.

As shown in FIGS. 8 and 11, on an outer surface of the bearing cap 68, apair of support brackets 68 b, 68 b project in an opposed manner at aposition offset to one side. A guide roller 71 is rotatably mounted onthe center of a support shaft 70 which has both end portions thereofsupported by the support brackets 68 b, 68 b in a penetrating manner,and the center axis of the derailleur shaft 81 forms a tangent of acircumferential circle of the guide roller 71.

A wire guide member 72 is mounted in a state that the wire guide member72 covers the periphery of the support brackets 68 b, 68 b and the guidecap 64.

The wire guide member 72 has the following construction as shown in FIG.11. Lower ends of side walls 72 a, 72 a which sandwich the supportbrackets 68 b, 68 b from outside are connected by a connecting portion72 b, one end surface of three sides of the side walls 72 a, 72 b andthe connecting portion 72 b forms a mating surface with the bearing cap68. As shown in FIG. 8, upper portions of the side walls 72 a, 72 aextend upwardly while being separated from the mating surface and areconnected thus forming a wire guide portion 72 c. A guide hole 72 d isformed in the wire guide portion 72 c in the oblique upward direction.

An end portion of the large-diameter outer tube 63 is fitted into anupper half portion of the guide hole 72 d, while the wire 62 penetratesa lower half portion of the guide hole 72 d having a small diameter. SeeFIG. 8.

The wire guide member 72 has axial holes at positions of the side walls72 a, 72 a which become coaxial with the pivotal mounting portions ofthe above-mentioned support brackets 68 b, 68 b. The support brackets 68b, 68 b are inserted between both side walls 72 a, 72 a and matingsurfaces are made to conform to an outer surface of the bearing cap 68.The guide roller 71 is inserted into the support brackets 68 b, 68 b,with the support shaft 70 penetrating all of the side wall 72 a, thesupport bracket 68 b and the guide roller 71 from the outside so as tomount the wire guide member 72 on the bearing cap 68 and, at the sametime, to pivotally support the guide roller 71.

As shown in FIG. 8, the derailleur arm 82 includes a first derailleurarm 83 and a second derailleur arm 84. A cylindrical slide member 85 isslidably fitted on an outer periphery of the derailleur shaft 81 in astate wherein the slide member 85 performs the translation in the centeraxial direction and the turning. Proximal end portions 83 a, 84 a of thefirst and second derailleur arms 83, 84 are fitted on an outer peripheryof the slide member 85 under pressure in parallel. A distal end portion83b of the first derailleur arm 83 and a boss portion 84b formed on thecenter of a flattened cylindrical portion 84 c formed on a distal end ofthe second derailleur arm 84 are fastened and are integrally connectedwith each other due to the threaded engagement of a guide pulley supportshaft 87 which constitutes a bolt while sandwiching a cylindrical collar89 therebetween and a nut 88.

As shown in FIGS. 8, 15 and 16, a drive sprocket wheel movementrestricting member 120 which is curved in an approximately semicircularshape is formed on an outer peripheral portion of the flattenedcylindrical portion 84 c of the second derailleur arm 84 in a statewherein the drive sprocket wheel movement restricting member 120 extendstowards the distal end of the second derailleur arm 84. The drivesprocket wheel movement restricting member 120 is integrally rotatedwith the derailleur arm 84 around the derailleur shaft 81 at selectedpositions between a position which is closest to the output shaft 14,indicated by a solid line, and a position which is remotest from theoutput shaft 14, indicated by a chain double-dashed line, as shown inFIG. 4.

Further, as indicated by a chain double-dashed line in FIG. 4, when thedrive sprocket wheel movement restricting member 120 is in a statewherein the drive sprocket wheel movement restricting member 120 assumesthe remotest position from the output 14, the drive sprocket wheelmovement restricting member 120 is formed into a shape that the innercenter of an approximately semicircular arch of the drive sprocket wheelmovement restricting member 120 is positioned at the pivot shaft 7 whichpenetrates the left and right casings 20L, 20R in the inside of thecasing 20, that is, a shape in which a radius of curvature of theapproximately semicircular arch has a substantially equal value as aradius of the guide pulley 86 of the derailleur 80.

As shown in FIG. 12 and FIG. 13, a cylindrical proximal portion 104 of atensioner arm 101 of a tensioner 100 is rotatably supported on an outerperiphery of the collar 89 through which the guide pulley support shaft87 penetrates, and a pair of first and second tensioner arms 102, 103extend from both end portions of the cylindrical proximal portion 104.

As shown in FIG. 8, the guide pulley 86 is rotatably supported on anouter periphery of the cylindrical proximal portion 104 by way of needlebearings 90.

As shown in FIG. 10, the manipulating pin 65 which penetrates a pair ofguide holes 81 a, 81 a of the derailleur shaft 81 further extends to theoutside from both rollers 66, 66, and then penetrates the slide member85, and has both ends thereof fitted on the proximal end portion 84 a ofthe second derailleur arm 84.

Further, the above-mentioned compression coil 91 is interposed betweenthe bearing cap 68 and the proximal end portion 83a of the firstderailleur arm 83 and biases the first and second derailleur arms 83, 84in the right direction.

As shown in FIG. 12 and FIG. 13, the tensioner 100 includes thetensioner arm 101 which has the cylindrical proximal portion 104 thereofpivotally supported on the guide pulley support shaft 87, a tensionerpulley 105 which is pivotally supported on a distal end of the tensionerarm 101, and a tensioner spring 106 which tilts and biases the tensionerarm 101 with respect to the derailleur arm 82.

The tensioner arm 101 includes first and second tensioner arms 102, 103and a tensioner pulley support shaft 108 which constitutes a boltpenetrates the first and second tensioner arms 102, 103 whilesandwiching an inner race of a bearing 107 between distal end portionsof the first and second tensioner arms 102, 103 and is threadedlyengaged with a nut 109 so as to fasten the first and second tensionerarms 102, 103. Further, the tensioner pulley 105 is fitted on an outerrace of the bearing 107 so as to rotatably and pivotally support thetensioner pulley 105 about the tensioner pulley support shaft 108.

Here, to explain in conjunction with FIGS. 4 and 8, projecting portions102 a, 103 a are formed in the vicinity of the proximal portions of thefirst and second tensioner arms 102, 103 with a collar 110 interposedbetween both projecting portions 102 a, 103 a. The projecting portions102 a, 103 a are integrally connected with each other due to thethreaded engagement of a bolt 111 and a nut 112.

As shown in FIGS. 4 and 5, the transmission chain 58 is wound around thedrive sprocket wheel 41 which is pivotally mounted on the crankshaft 11in the clockwise direction in FIG. 4 by way of the one-way clutch 42 andthe slide mechanism S. Thereafter, the transmission chain 58 is woundaround the tensioner pulley 105 in the clockwise direction. Thetransmission chain 58 passes between the bolt 111 and the guide pulley86 and is wound around the guide pulley 86 in the counter clockwisedirection. Thereafter, the transmission chain 58 is wound in theclockwise direction around any one of the transmission sprocket wheels51 to 57 and, thereafter, returns to the drive sprocket wheel 41 and iswound around the drive sprocket wheel 41.

A tensioner spring 106 includes a torsional coil spring, as shown inFIG. 12, and is accommodated in a flattened cylindrical portion 84 cformed on a distal end portion of the second derailleur arm 84 in astate wherein the tensioner spring 106 surrounds a center boss portion84 b. One end portion 106 a of the tensioner spring 106 is engaged withthe second derailleur arm 84, while another end portion 106 b of thetensioner spring 106 is engaged with the second tensioner arm 103. Dueto a spring force of the tensioner spring 106, the tensioner arm 101 isbiased in the clockwise direction about the guide pulley support shaft87 which includes a pivoting center shaft in FIG. 4 so as to push thetensioner pulley 105. Thus, a proper amount of tension is imparted tothe transmission chain 58 thus preventing the slackening of thetransmission chain 58.

Due to a reaction force of the spring force of the tensioner spring 106,in FIG. 4, a torque in the counter clockwise direction which brings thederailleur arm 82 provided with the guide pulley 86 close to the outputshaft 14 is generated.

A balancing spring 92 is interposed between the bearing cap 68 and thederailleur shaft 81 and is formed of a torsional coil spring which isprovided for imparting a torque to the derailleur arm 82 by way of theengagement of the guide holes 81 a, 81 a of the derailleur shaft 81 andthe manipulating pin 65. More specifically, as illustrated in FIG. 4,the balancing spring 92 serves to apply a balancing torque which isbalanced with the counter clockwise torque which is generated by thereaction force of the spring force of the above-mentioned tensionerspring 106. In this embodiment, a balancing torque in the clockwisedirection separates the derailleur arm 82 provided with the guide pulley86 from the output shaft 14 to the derailleur shaft 81.

Due to such a construction, when the derailleur arm 82 and the guidepulley 86 are moved in the axial direction to enable the changeover ofthe winding of the transmission chain 58 among the transmission sprocketwheels 51 to 57 which differ in the outer diameter in response to thetransmission manipulation of the transmission manipulating mechanism M2,it is possible to hold a tension imparted to the transmission chain 58to an optimum value in a following manner. Along with the axial movementof the derailleur arm 82, when the transmission chain 58 turns aroundthe derailleur shaft 81, the spring force of the tensioner spring 106 isincreased or decreased corresponding to the increase or decrease of thespring force of the balancing spring 92 which is changed along with thetilting of the derailleur arm 82. Thus, the tension applied to thetransmission chain 58 can be held at the optimum value.

To explain the operation in conjunction with FIGS. 8 and 11, a lowerportion of a cylindrical portion 22 t which constitutes the derailleurbearing hole 27L of the left reinforcing member 22L is partially notchedto expose a portion of the outer periphery of the bearing cap 68. Ascrew mounting boss 22 b is formed in a bulged manner along a notchedopening end surface of the cylindrical portion 22. A projection 68 c isformed on an exposed outer peripheral surface of the bearing cap 68which faces an end surface of the screw mounting boss 22 b. An adjustingbolt 73, which is threaded in the direction orthogonal to the derailleurshaft 81, penetrates the screw mounting boss 22 b with a distal end ofthe adjusting bolt 73 being brought into contact with a bulging portion68 c of the bearing cap 68.

Since a torque which acts on the derailleur shaft 81 due to the tensionof the transmission chain 58 acts on the bearing cap 68 by way of thebalancing spring 92, the projection 68 c of the bearing cap 68 isconstantly brought into pressure contact with a distal end of theadjusting bolt 73.

A nut 74 is threadedly engaged with the adjusting bolt 73, wherein afterthe rotary angle of the derailleur shaft 81 is adjusted. The nut 74 isthreaded with the adjusting bolt 73 and is brought into contact with thescrew mounting boss 22 b. Thus, the adjusting bolt 73 is fixed.

As shown in FIG. 8, a coil spring 76 is interposed between a headportion of the stopper bolt 75 and an opening end of the stopper bolthole 30, wherein the stopper bolt 75 is biased rightwardly by a springforce of the coil spring 76 and the stopper bolt 75 is fixed due to theincrease of a frictional force between male threads of the stopper bolt75 and female threads of the right reinforcing member 22R.

In conjunction with FIGS. 4, 12 and 13, the following explanation ismade with respect to a changeover movable range of the guide pulley 86and a moving path of the guide pulley 86 within the changeover movablerange which enable the changeover of winding of the transmission chain58 which is guided by the guide pulley 86 to respective transmissionsprocket wheels 51 to 57.

The above-mentioned changeover movable range of the guide pulley 86 bythe transmission manipulation of the transmission manipulation mechanism60 is defined by a first position, see FIG. 12, where the derailleur arm82 is brought into contact with the stopper bolt 75 due to the springforce of the compression coil spring 91 and a second position, see FIG.13, where the manipulating pin 65 moves the derailleur arm 82 leftwardlyso that the derailleur arm 82 is brought into contact with a washer 93which constitutes a stopper.

With respect to the above-mentioned changeover movable range, the axialdirectional range of the derailleur shaft 81 is set such that the guidepulley 86 assumes the axial directional positions equal to those of thetransmission sprocket wheel 57 having the minimum outer diameter and thetransmission sprocket wheel 51 having the maximum outer diameter whichare transmission sprocket wheels positioned at both axial end portionsof the transmission sprocket wheel body 50. The axial directional rangeof the derailleur shaft 81 is determined by the position of the stopperbolt 75 at the above-mentioned first position and the axial directionalposition of the washer 93 at the above-mentioned second position.

On the other hand, a rotation movable range about the derailleur shaftis set such that the guide pulley 86 occupies positions where the guidepulley 86 is radially and outwardly spaced apart by given distances fromthese transmission sprocket wheels 57, 51 corresponding to thetransmission sprocket wheel 57 having the minimum outer diameter and thetransmission sprocket wheel 51 having the maximum outer diameter. SeeFIG. 4.

The derailleur shaft 81 is supported on the casing 20 in a state whereinthe derailleur shaft 81 is rotatable with respect to the casing 20 andthe axial directional movement thereof is interrupted. Accordingly, withrespect to the rotational range of the derailleur shaft 81, the rotarypositions of the derailleur shaft 81 are determined based on thebalancing position where a shape of a spiral guide hole 81 a which isgently inclined, a torque Ta which acts on the derailleur shaft 81 byway of the manipulating pin 65 due to the spring force of the tensionerspring 106 which acts on the derailleur arm 82, and a balancing torqueTh which is generated by the spring force of the balancing spring 92 andacts on the derailleur shaft 81 balance with each other.

Accordingly, the shape of the spiral guide hole 81 a of the derailleurshaft 81 is, in view of the above-mentioned balancing of the torques,preliminarily designed such that the derailleur arm 82 is turned torespective given turning positions corresponding to respective axialpositions which correspond to the transmission sprocket wheels 51 to 57.

The irregularities exist with respect to both-end engaging positions ofthe balancing spring 92 immediately after assembling. Thus, an initialload of the balancing spring 92 does not agree with a given value.Accordingly, the initial adjustment is necessary and an adjustmentmethod thereof is explained hereinafter.

The above-mentioned peeping hole 28L formed in the left casing 20L isprovided at a position where the guide pulley support shaft 87 of theguide pulley 86 and the center axis of the peeping hole 28L arecoaxially aligned with each other when, as shown in FIG. 13, thederailleur arm 82 is positioned at an axial directional position whichcorresponds to the first-speed, minimum transmission ratio, with thetransmission sprocket wheel 51 having the largest outer diameter and isalso accurately positioned at given turning position, see chaindouble-dashed line in FIG. 4.

Accordingly, provided that the axial directional position and turningposition of the derailleur arm 82 are set to the given relationship,when the transmission ratio is set to a minimum value by manipulatingthe transmission manipulating member 61 of the transmission manipulatingmechanism 60, it is assumed that the guide pulley support shaft 87 canbe viewed with naked eyes by peeping the peeping hole 28L of the leftcasing 20L.

As mentioned previously, when the adjusting bolt 73 is rotated and isadvanced, the bearing cap 68 and the left end 92 b of the balancingspring 92 are turned in one direction or the reverse direction about thederailleur shaft 81, and the balancing spring 92 is reeled in or reeledout so that the initial load of the balancing spring 92 is increased ordecreased whereby the torque Tb which acts on the derailleur shaft 81 byway of the balancing spring 92 is changed as mentioned above. Theinitial rotary angle of the derailleur shaft 81 is adjusted under thebalancing of the torque Th and the torque Ta which acts on thederailleur shaft 81 due to the tension of the transmission chain 58,whereby the derailleur arm 82 is turned by way of the manipulating pin65 due to the rotation of the derailleur shaft 81.

Accordingly, by setting the transmission ratio to the minimum value bymanipulating the transmission manipulating member 61 after assembling,the threaded engagement state of the adjusting bolt 73 is adjusted bypeeping the peeping hole 28L of the left casing 20L. See FIG. 2.

When the adjusting bolt 73 is rotatably manipulated, the derailleur arm82 is turned simultaneously with the guide pulley support shaft 87.Thus, the adjusting bolt 73 is rotatably manipulated such that the guidepulley support shaft 87 can be viewed through the peeping hole 28L bypeeping the peeping hole 28L.

A state in which the adjustment is completed is shown in FIG. 13 and isindicated by a chain double-dashed line in FIG. 4.

In this manner, provided that the initial adjustment of the rotationalangle of the derailleur shaft 81 is properly performed when thetransmission ratio is at a minimum, since the shape of the guide hole 81a of the derailleur shaft 81 is preliminarily designed by taking thebalancing of the torque into consideration, the rotational angles of thederailleur shaft 81 at respective other transmission ratios can beautomatically set to given angles, respectively. Thus, it is possible toturn the derailleur arm 82 and the guide pulley 86 to respective turningpositions corresponding to respective axial positions which correspondto the transmission sprocket wheels 51 to 57.

After completion of the initial adjustment, the cap 96 is fitted in thepeeping hole 28L to plug the peeping hole 28L.

As described above, by performing the rotational manipulation of theadjusting bolt 73 such that the guide pulley support shaft 87 can beobserved with the naked eyes while peeping at the peeping hole 28L, itis possible to accurately and simply set the axial directional positionand the turning direction of the derailleur arm 82 to given positions.

Next, the slide restricting structure of the drive sprocket wheel body40 is explained. FIG. 14 is a cross-sectional developed view taken alonga line XIV-XIV in FIG. 4. That is, FIG. 14 is a developed view of across-section including the crankshaft 11, the guide pulley supportshaft 87 and the derailleur shaft 81.

FIG. 15 is a right side view of the above-mentioned second derailleurarm 84 and FIG. 16 is a cross-sectional view taken along a line XVI-XVIin FIG. 15. As shown in FIG. 15, a drive sprocket wheel position settingmember 120 is curved in an arcuate shape and extends from an outerperipheral portion of the flattened cylindrical portion 84 c. The drivesprocket wheel position setting member 120 is a member which restrictsthe slide movement of the drive sprocket wheel 41 and is integrallyformed with the second derailleur arm 84.

The derailleur arm 82 is rotated together with the drive sprocket wheelposition setting member 120 about the derailleur shaft 81 in response tothe transmission manipulation and assumes selected positions between aposition, indicated by a solid line, where the derailleur arm 82 isarranged closest to the output shaft and a position, indicated by animaginary line, where the derailleur arm 82 is arranged remotest fromthe output shaft as viewed from the right side in the axial direction ofthe output shaft.

In the state wherein the drive sprocket wheel position setting member120 assumes the position where the member 120 is remotest from theoutput shaft 14, the pivot shaft 7 assumes a state in which the pivotshaft 7 is positioned at the inner center of an arch of the drivesprocket position setting member 120.

In a lower half portion of FIG. 14, the crankshaft 11 is provided withthe drive sprocket wheel body 40 of the transmission mechanism M1,wherein the drive sprocket wheel body 40 includes the one-way clutch 42,the slide mechanism S, the drive sprocket wheel 41, the transmissionchain removal preventing chain guides 47, and the drive sprocketmovement restricting member 121 which restricts the movement of thedrive sprocket wheel. As mentioned previously, the above-mentioned chainguides 47 are mounted on both sides of a tip portion of the drivesprocket wheel 41 using rivets 49.

FIG. 17 is a right side view of the above-mentioned drive sprocket wheelmovement restricting member 121 and FIG. 18 is a cross-sectional viewtaken along a line XVIII-XVIII in FIG. 17. Using rivets 125 whichpenetrate a rivet hole 122 formed in a flange portion 45 c of the outersleeve 45, a rivet hole 123 formed in the drive sprocket wheel 41 and arivet hole 124 formed in the drive sprocket wheel movement restrictingmember 121, the drive sprocket wheel movement restricting member 121 isintegrally mounted on a right side of the above-mentioned drive sprocketwheel 41 concentrically with the drive sprocket wheel.

As shown in FIG. 4, in a side view, the drive sprocket wheel positionsetting member 120 is positioned to be overlapped with the drivesprocket wheel movement restricting member 121 between a distal end of acurved portion to an approximately intermediate portion of the arch. Thedistal end of the drive sprocket wheel position setting member 120 isarranged at an approximately intermediate portion of a line whichconnects the crankshaft 11 and the guide pulley support shaft 87 of thederailleur 80.

The alignment mechanism of the transmission chain is hereinafterexplained. As illustrated in FIG. 4, in a path of the transmission chainextends and is wound around the reel-out side of the transmissionsprocket wheel and the reel-in side of the above-mentioned drivesprocket wheel with a chain guide member 130 which aligns thetransmission chain being provided.

FIG. 19 is a right side view showing only members which are relevant tothe transmission chain alignment in the inside of the casing 20 forindicating the relative positional relationship among theabove-mentioned transmission sprocket wheel body 50, the drive sprocketwheel 41 and the chain guide member 130. FIG. 20 is a side view of theabove-mentioned chain guide member 130, and FIG. 21 is an upper planview of the chain guide member 130. The above-mentioned chain guidemember 130 is made of synthetic resin and includes an upper guideportion 131 which is arranged above the chain path, a lower guideportion 132 which is arranged below the chain path, and a verticalconnecting portion 133 which connects the above-mentioned guideportions.

The upper guide portion 131 constitutes an upper movement restrictingmember of the transmission chain 58 and the lower guide portion 132 is alower movement restricting member of the transmission chain 58, whereinthe above-mentioned members are integrally connected by the verticalconnecting portion 133 to constitute a single part. Two bolt holes 134are formed in the vertical connecting portion 133. As shown in FIG. 21,the chain guide member 130 is fixed to the left reinforcing member 22Lof the casing 20L by way of bolts 137 which are inserted into these boltholes 134.

The chain guide member 130 is, as shown in FIGS. 4 and 19, arranged at amiddle portion between the transmission sprocket wheel body 50 and thedrive sprocket wheel 41, as viewed in a side view, the above-mentionedupper guide portion 131 is provided at a position where the upper guideportion 131 is overlapped to the multi-stage transmission sprocketwheels 50.

Transmission-chain-delivering-side surfaces of the upper and lower guidemembers 131, 132 are arranged parallel to each other as viewed in thetransmission chain moving direction and are formed to have a widthsufficient to allow the transmission chain 58 to pass between the upperand lower guide portion 131, 132.

As shown in FIG. 21, an oblique comb-teeth-like portion 135 is formed ona distal end of the upper guide member 131 on atransmission-sprocket-wheel-body 50 side. The respective comb teeth areinserted into gaps formed between tips of respective transmissionsprocket wheels 51 to 57. At the time of changing over the transmissionchain, the transmission chain 58 is surely removed from any one of thetransmission sprocket wheels 51 to 57 with which the transmission chain58 being meshed and the transmission chain 58 being returned in thedirection toward the drive sprocket wheel 41.

As shown in FIG. 20, on a drive-sprocket-wheel side of the chain guidemember 130, a throat portion 136 which narrowly restricts the verticalposition of the passing transmission chain 58 is provided. This throatportion 136 is a portion which narrows a vertical width of thetransmission chain path.

Next, the manner of operation and advantageous effects of the embodimenthaving the above-mentioned construction are hereinafter explained.

As indicated by the solid line in FIG. 4 and as shown in FIGS. 5, 8 and12, in a state wherein the transmission sprocket wheel 57 is selected asan operating sprocket wheel among the group of the transmission sprocketwheels 51 to 57 by the derailleur 80 having the derailleur arm 82provided at the above-mentioned first position, that is, when theseventh-speed position is selected as the transmission position, due tothe crankshaft 11 which is rotated in the advancing direction P as therider turns the pedals 12, the drive sprocket wheel 41 is rotatablydriven in the advancing direction P by way of the one-way clutch 42 andthe slide mechanism S.

Due to the drive sprocket wheel 41 which is rotatably driven in theadvancing direction P, the transmission sprocket wheel 57, the outputshaft 14 and the rear wheel drive sprocket wheel 15 are rotatably drivenat the high-speed-side maximum transmission ratio which is determined byboth sprocket wheels 41, 57 by way of the transmission chain 58.

The power of the crankshaft 11, which is rotatably driven by the rider,is transmitted to the output shaft 14 by way of the drive sprocket wheel41, the transmission chain 58 and the transmission sprocket wheel 57.Thus, the power of the output shaft 14 is transmitted to the rear wheelWr by way of the above-mentioned drive force transmission mechanismwhereby the bicycle B travels at the seventh-speed position.

To change over the transmission position from the above-mentioned statewhich assumes the seventh-speed position using the derailleur 80, whenthe transmission manipulating member 61 is manipulated to select thelow-speed-side transmission sprocket wheel, for example, thetransmission sprocket wheel 51 as the operating sprocket wheel, due tothe wire 62 which is moved leftwardly in the derailleur axial directionin FIG. 12, the manipulating pin 65 which is guided by the guide hole 81a is moved toward a left-side peripheral portion 61 g of the guide hole81 a.

Here, the derailleur arm 82 and the guide pulley 86 which are integrallymoved with the manipulating pin 65 are moved on the derailleur shaft 81leftwardly along the axis in FIG. 12. At the same time, the derailleurarm 82 and the guide pulley 86 are rotated in the clockwise directionabout the derailleur shaft 81 in FIG. 4. At a point in time when thederailleur arm 82 comes into contact with the washer 93 (see FIG. 13),the alignment mechanism assumes the first-speed position which is thetransmission position indicated by a chain double-dashed line in FIG. 4.

Here, a state of the pin 61 p is indicated by a chain double-dashed linein FIG. 10.

Thereafter, the winding of the transmission chain 58 which is movedleftwardly in FIG. 12 together with the guide pulley 86 is changed overfrom the transmission sprocket wheel 57 to the transmission sprocketwheel 51, sequentially, by way of the sprocket wheels 56 to 52 halfway.Thus, the transmission sprocket wheel 51 is drivably connected with thedrive sprocket wheel 41 by way of the transmission chain 58 as shown inFIG. 13.

The drive sprocket wheel 41, which is movable in the crankshaft axialdirection by the slide mechanism S shown in FIGS. 5 and 6, is moved inthe axial direction of the crankshaft 11 due to acrankshaft-axial-directional component of tension of the transmissionchain 58 and assumes a position indicated by a chain double-dashed linein FIG. 14.

Further, the tensioner pulley 105 assumes a position where the tensionerpulley 105 imparts a proper amount of tension to the transmission chain58 using the tensioner spring 106. See a chain double-dashed line inFIG. 4.

Further, when the wire 62 is slackened by manipulating the transmissionmanipulating member 61 and any one of the high-speed-side transmissionsprocket wheels 52 to 57 is selected which exhibit a higher speed thanthe transmission sprocket wheel 51 is selected as the operating sprocketwheel, the derailleur arm 82 is moved rightwardly due to the springforce of the compression coil spring 91. At the same time, the guidepulley 86 selects any one of the high-speed-side transmission sprocketwheels 52 to 57 and the winding of the transmission chain 58 is changedover to the above-mentioned selected operating sprocket wheel.

Also in this case, along with the movement of the derailleur arm 82, thedrive sprocket wheel 41 is moved to the position which corresponds tothe new transmission position in the crankshaft axial direction by wayof the transmission chain 58.

Thereafter, the bicycle B travels with the transmission ratio at the newtransmission position.

In short, in changing over the transmission position, when thetransmission manipulating member 61 is manipulated, the derailleur arm82, and the guide pulley 86, the tensioner pulley 105 are moved to thedesired transmission positions. Thereafter, the operating sprocket wheelselected from the group of sprocket wheels 51 to 57 and the drivesprocket wheel 41 on the crankshaft are connected with each other by wayof the transmission chain 58 by means of the derailleur 80.

Due to the crankshaft-axial directional component of the tension of thetransmission chain 58, the drive sprocket wheel 41 is moved along thecrankshaft and assumes the position which corresponds to theabove-mentioned selected operating sprocket wheel.

The wire 62 which is inserted into the guide hole 72 d of the wire guidemember 72 is wound around the guide roller 71 and is inserted into theinside of the derailleur shaft 81 from the small hole formed in theguide cap 64. Accordingly, irrespective of the direction that the wire62 is inserted into the guide hole 72 d from the outside, the wire 62which is once inserted into the guide hole 72 d is surely rightly woundaround the guide roller 71 orthogonal to the support shaft 70, and isinserted into the derailleur shaft 81 while being accurately alignedwith the center axis of the derailleur shaft 81 whereby the wire 62 canbe smoothly advanced and retracted.

Due to the advancing and retracting of the wire 62 bought about by themanipulation of the transmission manipulating member 61, themanipulating pin 65 is moved in the inside of the derailleur shaft 81 inthe axial direction together with the rollers 66, 66 by way of theconnecting hook 67.

Since the pair of rollers 66, 66 which are pivotally supported on themanipulating pin 65 are respectively rotatably fitted in the guide holes81 a, 81 a formed in the derailleur shaft 81, due to the movement of themanipulating pin 65 in the axial direction, the manipulating pin 65 perse is turned by being guided by the guide holes 81 a, 81 a. At the sametime, the derailleur arm 82 and the guide pulley 86 can be turnedintegrally with the manipulating pin 65 with respect to the derailleurshaft 81 and can be moved in the axial direction simultaneously.

Since the manipulating pin 65 is fitted in the guide holes 81 a, 81 a byway of the rollers 66, 66, when the manipulating pin 65 is moved whilebeing guided by the guide holes 81 a, 81 a, the rollers 66, 66 roll inthe directions opposite to each other. Thus, the frictional resistanceis largely reduced thus making the movement of the manipulating pin 65smooth whereby the transmission operation can be performed smoothly.

Since the derailleur shaft 81 is not fixed to the casing 20 and isconfigured to be rotatable and biased by the balancing spring 92, evenwhen an excessive torque acts on the derailleur shaft 81 from themanipulating pin 65 by way of the derailleur arm 82, the derailleurshaft 81 is rotated so that the excessive torque is alleviated.

Since the torque which acts on the derailleur shaft 81 due to thetension of the transmission chain 58 acts on the bearing cap 68 by wayof the balancing spring 92, the projection 68 c of the bearing cap 68 isconstantly pushed to the distal end of the adjusting bolt 73.

Accordingly, when the adjusting bolt 73 is advanced or retracted due tothe rotation of the adjusting bolt 73, the bearing cap 68 is rotatedabout the center axis of the derailleur shaft 81 by way of theprojection 68c of the bearing cap 68 which is fitted in the derailleurbearing hole 27L.

The rotation of the bearing cap 68 rotates the derailleur shaft 81 byway of the balancing spring 92 so as to adjust the rotating angle of thederailleur shaft 81.

The adjustment of the rotating angle of the derailleur shaft 81 isperformed by peeping the peeping hole 28L formed in the left casing 20Lin a state that the derailleur arm 82 is arranged closest to the leftcasing 20L as shown in FIG. 13 when the transmission ratio is a minimum.Accordingly, the user can easily observe the guide pulley support shaft87 and can easily adjust the guide pulley support shaft 87.

Further, in this embodiment, when the stopper bolt 75 is threadedlyengaged with the stopper bolt hole 30(see FIG. 3) which is formed in thevicinity of the derailleur bearing hole 27R formed in theabove-mentioned right reinforcing member 22R, the distal end of thestopper bolt 75 which is threadedly engaged in parallel to thederailleur shaft 81 projects into the inside of the casing 20 and cancome into contact with the proximal end portion 84 a of the secondderailleur arm 84. See FIG. 8. More specifically, based on a threadedengagement amount of the stopper bolt 75, it is possible to adjust arightward movable limit of the derailleur arm 82.

Further, since the peeping hole 28R is formed in the above-mentionedright casing 20R, when the derailleur arm 82 is accurately positioned atthe axial position corresponding to the transmission sprocket wheel 57of the seventh-speed (maximum transmission ratio) having the minimumouter diameter and at the given turning position as shown in FIG. 13, itis possible to make the guide pulley support shaft 87 of the guidepulley 86 and the center axis coaxially aligned with each other. See achain double-dashed line in FIG. 3.

Accordingly, as shown in FIG. 3, it is possible to adjust the threadedengagement state of the stopper bolt 75 while peeping the peeping hole28R formed in the right casing 20R such that the rotational angle of thederailleur arm 82 is stopped at a given angle when the transmissionratio is set to a maximum value by manipulating the transmissionmanipulating member 61 after the above-mentioned adjustment.

When the stopper bolt 75 is advanced or retracted due to the rotationalmanipulation thereof, it is possible to move the derailleur arm 82 whichis biased by the compression coil spring 91 in the axial direction. Dueto this axial movement of the derailleur arm 82, the derailleur arm 82is guided and turned in the guide hole 81 a formed in the derailleurshaft 81 by way of the manipulating pin 65. Thus, it is possible toperform the adjustment of the rotating angle by peeping the peeping hole28R.

In this manner, it is possible to accurately set the axial position ofthe derailleur arm 82 when the transmission ratio is set to the maximumvalue by restricting the axial position using the stopper bolt 75.

After completion of this setting, the cap 97 is fitted into the peepinghole 28R to plug the peeping hole 28R.

Due to the manipulation of the transmission manipulating member 61described above, it is possible to perform an adjustment such that thederailleur arm 82 and the guide pulley 86 are, respectively, turned tothe given turning positions corresponding to the respective axialpositions corresponding to the transmission sprocket wheels 51 to 57.Thus, the transmission operation can be smoothly performed.

More specifically, when the transmission manipulating member 61 ismanipulated and the manipulating pin 65 which is connected to the wire62 is moved in the axial direction to perform the changeover of thewinding of the transmission chain 58 to the low speed (or the highspeed) side, the manipulating pin 65 is guided by the guide hole 81 aformed in the derailleur shaft 81 whose rotational angle is determinedby the balancing of the torque and is turned together with thederailleur arm 82 and, at the same time, is moved in the axialdirection. Accordingly, the transmission chain 58 which is guided by theguide pulley 86 which moves along with the derailleur arm 82 is woundaround the transmission sprocket wheel which is alternatively selectedout of the group of the transmission sprocket wheels 51 to 57 inresponse to the transmission position whereby the drive sprocket wheel41 and the above-mentioned transmission sprocket wheel are drivablyconnected with each other by the transmission chain 58.

As described above, the adjustment of the derailleur shaft 81 and thesetting of the axial position of the derailleur arm 82 can be performedfrom the outside without disassembling the casing 20 after assemblingthe transmission T to the frame F. Thus, the assembling of thetransmission T is facilitated.

Further, since the peeping holes 28L, 28R are plugged with the caps 96,97, the inside of the casing 20 is hermetically sealed. Thus, thealignment mechanism hardly receives any disturbance.

Here, the peeping holes 28L, 28R, which constitute peeping windowsformed in the casing 20, may be formed by fitting a transparent membermade of glass or the like therein. In this case, it is possible tomaintain the sealing performance and, at the same time, it is no longernecessary to perform an operation to remove and fit the cap each time.

The bicycle B on which the transmission of the present invention ismounted is a downhill bicycle which is used in a competition in whichplayers compete against time spent for descending an unpaved coursewhich includes high-speed corners and jump sections in a woodland pathor the like. Accordingly, when the bicycle B turns a sharp curvelaterally, the transmission chain 58 which is wound around the drivesprocket wheel body 40 and the transmission sprocket wheel body 50receives a centrifugal force in the direction opposite to the directionthat the bicycle B turns. Thus, the transmission chain 58 is liable tobe removed from the teeth of the drive sprocket wheel 41 of the drivesprocket wheel body 40 in the centrifugal direction. Alternatively, thebicycle B is vigorously jolted vertically due to the unevenness of atraveling surface at the time of traveling. Thus, the transmission chain58 is liable to be removed from the drive sprocket wheel 41. However, asshown in FIGS. 5 and 14, the chain guides 47 are integrally formed onboth sides of the outer peripheral portion of the drive sprocket wheel41. Thus, it is possible to preliminarily prevent the transmission chain58 from being removed from the drive sprocket wheel 41 due to the chainguides 47.

Further, due to the tension of the transmission chain 58 which is woundaround the drive sprocket wheel 41, the drive sprocket wheel body 40receives a confining force which prevents the movement of the drivesprocket wheel body 40 in the axial direction of the crankshaft 11. Inthis case, when the centrifugal force, which is generated when thebicycle B travels the sharp curve, is large, there may be a case whereinthe drive sprocket wheel 41 and the outer sleeve 45 which constituteaxially movable portions of the drive sprocket wheel body 40 may move inthe centrifugal force direction by overcoming the confining force.However, even in such a case, as shown in FIG. 14, the drive sprocketwheel position setting member 120 is integrally formed with thederailleur arm 82 whose axial position is set by the derailleur 80, thedrive sprocket wheel movement restricting member 121 is integrallymounted on the right side of the drive sprocket wheel 41, and the drivesprocket wheel position setting member 120 is positioned between thedrive sprocket wheel 41 and the drive sprocket wheel movementrestricting member 121. Accordingly, when the drive sprocket wheel 41,the outer sleeve 45 and the drive sprocket wheel movement restrictingmember 121 which constitute the movable portions of the drive sprocketwheel body 40 are made to move leftwardly, for example, due to theabove-mentioned centrifugal force, and the drive sprocket wheel movementrestricting member 121 is brought into contact with the drive sprocketwheel position setting member 120. Thus, the leftward movement of themovable portions of the drive sprocket wheel body 40 is obstructed.Further, when the movable portions of the drive sprocket wheel body 40are made to move rightwardly due to the above-mentioned centrifugalforce, the chain guide members 47 which are integrally formed with thedrive sprocket wheel 41 are brought into contact with the drive sprocketwheel position setting member 120. Thus, the rightward movement of themovable portions of the drive sprocket wheel body 40 is obstructed.

Due to the slide restriction structure which includes the drive sprocketwheel position setting member 120 and the drive sprocket wheel movementrestricting member 121, the axial position of the drive sprocket wheel41 is constantly restricted within the given range with respect to theguide pulley 86 and the tensioner pulley 105. Thus, the transmissionchain 58 is returned along the rotational surfaces of the drive sprocketwheel 41, and the tensioner pulley 105 and the given sprocket of thetransmission sprocket wheels 51 to 57. Thus, the transmission chain 58is stably meshed with these sprocket wheels. As a result, it is possibleto surely prevent the removal of the transmission chain 58 from thesesprocket wheels and, at the same time, the transmission chain 58 can besmoothly returned whereby the high transmission efficiency is obtained.

Thereafter, drive sprocket wheel position setting member 120 which isbranched from the outer peripheral portion of the flattened cylindricalportion 84 c to the radial direction is curved in the clockwisedirection in FIG. 4. Thus, even when the derailleur arm 82 of thederailleur 80 is tilted in a wide range as indicated by a solid line anda chain double-dashed line in FIG. 4 corresponding to the change of theradii of the transmission sprocket wheel 51 having the maximum diameterand transmission sprocket wheel 57 having the minimum diameter, there isno possibility that the drive sprocket wheel position setting member 120collides with the pivot shaft 7.

Further, since the drive sprocket wheel position setting member 120 iscurved as mentioned above, there exists no substantial differencebetween the engagement state of the drive sprocket wheel 41 and thering-like drive sprocket wheel movement restricting member 121 in astate indicated by the solid line in FIG. 4 where the derailleur arm 82is substantially directed to the crankshaft 11 which constitutes thecenter of rotation of the drive sprocket wheel 41 and the engagementstate of the drive sprocket wheel 41 and the ring-like drive sprocketwheel movement restricting member 121 in a state where the derailleurarm 82 is indicated by the chain double-dashed line in FIG. 4. As aresult, the drive sprocket wheel position setting member 120 canmaintain a fixed contact state with respect to the drive sprocket wheel41 and the drive sprocket wheel movement restricting member 121.

Further, since the outer peripheral portion 126 of the drive sprocketwheel movement restricting member 121 is formed in a circular ringshape, the contact state of the drive sprocket wheel movementrestricting member 121 with respect to the drive sprocket wheel positionsetting member 120 is fixed.

Still further, since the drive sprocket wheel movement restrictingmember 121 has an inversely V-shaped connecting portion 127 whichextends from the ring-like outer peripheral portion 126 to the centerdirection integrally formed thereon, the drive sprocket wheel movementrestricting member 121 can be made light-weighted.

In the bicycle B which mounts the transmission T thereon, the rotationalforce of the crankshaft 11 in the normal direction P which is generatedby rotating the pedals 12 rotatably drives the crankshaft 11, the drivesprocket wheel 41, the transmission chain 58, the transmission sprocketwheel body 50, the output shaft 14, the rear wheel drive sprocket wheel15, the rear wheel drive chain 17, the rear wheel driven sprocket wheel16, and the rear wheel Wr in this order. Thus, the rear wheel Wr isdriven and the bicycle B is advanced. In this case, the one-way clutch42 is provided relative to the drive force transmission path and theone-way clutch 42 is arranged between the crankshaft 11 and the drivesprocket wheel 41. Thus, when the crankshaft 41 is rotated in thereverse direction, the reverse rotation of the crankshaft 11 is nottransmitted to the drive sprocket wheel 41 and succeeding parts in theabove-mentioned order.

When the crankshaft 11 is reversely rotated or stopped during thetraveling of the bicycle, the bicycle advances with inertia. Moreparticularly in descending an inclined ground, the bicycle continues theadvancing. Thus, the rotation of the rear wheel Wr of the bicycle iscontinued. At this point of time, the rotation of the rear wheel Wr ofthe bicycle is directly transmitted to the transmission sprocket wheelbody 50 in the following order of the rear wheel Wr, the rear wheeldriven sprocket wheel 16, the rear wheel drive chain 17, the rear wheeldrive sprocket wheel 15, the output shaft 14 and the transmissionsprocket wheel body 50.

The transmission chain 58 extends between and is wound around thetransmission sprocket wheel body 50 and the drive sprocket wheel 41,wherein the drive sprocket wheel 41 which does not yet receive the driveforce from the crankshaft 11 is in a state wherein the drive sprocketwheel 41 is passively rotatable and the tension is applied to thetransmission chain 58 due to the balance between the tensioner spring106 of the chain tensioner 100 and the balancing spring 92. However,when the traveling road is undulated at a small pitch or when the riderstrongly steps on the pedals 39 and, thereafter, rapidly stops thestepping of the pedals 39, as shown in FIG. 19, the transmission chain58 is pushed into the reel-in side of the drive sprocket wheel body 40from the lower reel-out side of the transmission sprocket wheel body 50.Thus, the transmission chain 58 is deflected or slackened thus givingrise to a case wherein the meshing of the drive sprocket wheel 41 withthe reel-in side of the drive sprocket wheel 41 cannot be performedsmoothly.

The chain guide member 130 is provided for preventing such a seizure ofthe transmission chain 58. In the transmission T which includes thechain guide member 130 of this embodiment, as shown in FIG. 19, it ispossible to allow the transmission chain 58 which is slackened on thetransmission-sprocket-wheel-body-50 side of the chain guide member 130to be aligned in a straight line at the throat portion 136 and tosmoothly enter the drive sprocket wheel 41.

Accordingly, when the bicycle descends an unpaved course such ashigh-speed corners, jump sections and the like arranged in woodland orthe like, the bicycle B repeats the violent up-and-down movement. Thus,the vibration attributed to the inertial in the up-and-down direction isimparted. In the bicycle on which the chain guide member is mounted,even when the violent up-and-down movement takes place in the state inwhich the transmission chain 58 is deflected or slackened in theabove-mentioned manner, there is neither the possibility that theentrance of the drive sprocket wheel is clogged with the transmissionchain 58 due to the inertial vibration of the transmission chain in theup-and-down direction nor the possibility that the transmission chain 58is seized in the drive sprocket wheel 41.

As shown in FIG. 21, the chain guide member 130 is fixed to the leftreinforcing member 22L of the casing 20L using bolts 137 which areinserted into the bolt holes 134 and the chain guide member 130 is madeof synthetic resin. Thus, the chain guide member 130 can be manufacturedat a low cost and is light-weighted.

The chain guide member 130 is, as shown in FIGS. 4 and 19, arrangedbetween the transmission sprocket wheel body 50 and the drive sprocketwheel 41.

The transmission-chain-delivering-side surfaces of the upper and lowerguide members 131, 132 are arranged parallel to each other as viewed inthe transfer chain moving direction and are formed to have a sufficientwidth. Thus, when the transmission chain 58 is moved in the axialdirection of the output shaft at the time of changing over the windingof the transmission chain 58, it is possible to smoothly guide thetransmission chain 58.

As shown in FIG. 21, the oblique comb-teeth-like portion 135 is formedon the distal end of the upper guide member 131 on thetransmission-sprocket-wheel-body-50 side and the respective comb teethare inserted into gaps formed between the respective overlappedtransmission sprocket wheels 51 to 57. Accordingly, even at the time ofchanging over the winding of the transmission chain, it is possible toensure the restriction of the upward movement of the transmission chain58. Thus, the transmission chain 58 can be smoothly returned in thedirection toward the drive sprocket wheel 41.

As shown in FIG. 20, on the drive-sprocket-wheel side of the chain guidemember 130, the throat portion 136 which narrowly restricts the verticalposition of the passing transmission chain 58 is provided. Thetransmission chain which is delivered from the throat portion can arriveat the tip position of the drive sprocket wheel 41 in a tangentialmanner.

FIG. 22 to FIG. 26 are views showing a chain alignment mechanismaccording to the second embodiment of the present invention, whereinFIG. 22 is a right side view of only members which are relevant to thetransmission chain alignment in the inside of a casing. FIG. 23 is aside view of a chain guide member 140 in the above-mentioned secondembodiment. FIG. 24 is a cross-sectional view taken along a line XXIV-XXIV in FIG. 23. FIG. 25 is a cross-sectional view taken along a lineXXV- XXV in FIG. 23. FIG. 26 is a cross-sectional view taken along aline XXVI-XXVI in FIG. 23,

The chain guide member 140 of this embodiment is made of synthetic resinand is constituted of an upper guide portion 141 which is arranged abovea chain path, a lower guide portion 142 which is arranged below thechain path, vertical connecting portions 143 which connect theabove-mentioned guide portions, and a roller 147. The verticalconnecting portions 143 are provided on both sides, while the roller 147is rotatably held by a roller shaft 148, which is supported by extendingportions of the left and right vertical connecting portions 143 by wayof ball bearings 149. The roller shaft 148 is, as shown in FIG. 26,configured to be inserted into roller shaft holes 151 formed in theextending portions of the vertical connecting portions 143 arranged onleft and right sides of the roller shaft 148. Further, as shown in FIG.25, the roller shaft 148 is inserted into holes formed in left and rightreinforcing members 22L, 22R of the casing 20 and is supported by theleft and right reinforcing members 22L, 22R.

The chain guide member 140 is, as shown in FIG. 24, mounted on the leftreinforcing member 22L of the casing 20 by means of mounting bolts 150A,150B.

As shown in FIG. 24, an oblique comb-teeth-like portion 145 is formed ona distal end of the upper guide member 141 on thetransmission-sprocket-wheel-body-50 side. The respective comb teeth areinserted into gaps formed between tips of respective transmissionsprocket wheels 51 to 57. Accordingly, even at the time of changing overthe winding of the transmission chain, the transmission chain 58 issurely removed by any one of the transmission sprocket wheels 51 to 57with which the transmission chain 58 is meshed and the transmissionchain 58 is returned in the direction toward a drive sprocket wheel 41.

Since the chain alignment mechanism of this second embodiment has theabove-mentioned construction, as shown in FIG. 22, the roller 147 isalways brought into contact with the transmission chain 58 and hence,the tension is always applied to the transmission chain 58 between theroller 147 and the drive sprocket wheel 41 whereby the slackenedtransmission chain 58 is aligned in a straight line and can smoothlyenter the drive sprocket wheel 41.

In the transmission mechanism M1 which has been described in detailheretofore, the drive sprocket wheel body is constructed of asingle-stage sprocket wheel and the driven sprocket wheel body isconstituted of multi-stage sprocket wheels. This construction may bereversed. That is, in the transmission mechanism M1, the drive sprocketwheel body may be constructed of multi-stage sprocket wheels and thedriven sprocket wheel body may be constructed of a single-stage sprocketwheel. As a matter of course, corresponding to the change of the numberof stages of sprocket wheels, the construction of the transmissionchangeover mechanism M2 is also changed. Particularly, with respect tocomb teeth of a comb-teeth-like portion substantially equal to thecomb-teeth-like portions 135, 145 which are provided to theabove-mentioned chain guide members 130, 140, it is necessary to insertthese teeth into gaps between the respective transmission sprocketwheels which constitute the multi-stage sprocket wheels. Accordingly,when the stage construction of sprocket wheels of the transmissionmechanism is reversed in the above-mentioned manner, the comb-teeth-likeportion are formed on the lower guide portion which is arranged close tothe drive sprocket wheel, while the lower guide portion appears to beoverlapped to the drive sprocket wheel in a side view contrary to theembodiment shown in FIG. 19 and FIG. 22.

To consider a modification of such a construction, the comb-teeth-likeportion formed on one side of the chain guide member is inserted intogaps between respective sprocket wheels of either one of the drivesprocket wheel body or the driven sprocket wheel body which isconstituted of multi-stage sprocket wheels. Accordingly, in a side view,there arises a state in which either one of the upper or lower guideportions of the chain guide member is overlapped to either one of thedrive sprocket wheel or the driven sprocket wheel. By overlapping themembers in this manner, the chain alignment mechanism can effectivelymake use of the space and at the same time, can be made compact.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A chain alignment structure for a bicycle transmission, comprising: adrive sprocket wheel, said drive sprocket wheel being rotatably drivableby a crankshaft; a driven sprocket wheel, said driven sprocket wheelbeing drivably connectable with an output shaft that is rotated in aninterlocking manner with a drive wheel of the bicycle; and an endlesschain, said endless chain being wound around the drive sprocket wheeland the driven sprocket wheel, wherein a chain guide member is arrangedon an endless-chain-reel-in side of the drive sprocket wheel.
 2. Thechain alignment structure for a bicycle transmission according to claim1, wherein the driven sprocket wheel is configured to be alwaysintegrally rotated with the output shaft, and a one-way clutch whichtransmits rotation in the normal direction of the crankshaft to thedrive sprocket wheel is arranged between the crankshaft and the drivesprocket wheel.
 3. The chain alignment structure for a bicycletransmission according to claim 1, wherein the chain guide memberincludes a pair of guide portions which are arranged substantially inparallel with a transmission locus of the chain in a state that theguide portions sandwich the chain, and the pair of guide portions areconnected with each other by way of a connecting portion.
 4. The chainalignment structure for a bicycle transmission according to claim 1,wherein the driven sprocket wheel and the drive sprocket wheel arecovered with a single casing which is fixed to the vicinity of thecrankshaft, and the chain guide member is fixed in the inside of thecasing.
 5. The chain alignment structure for a bicycle transmissionaccording to claim 1, wherein there are a plurality of driven sprocketwheels which differ in diameter and are coaxially mounted on the outputshaft, a winding changeover unit which changes over the winding amongthe plurality of driven sprocket wheels around which the endless chainis wound is provided, and the chain guide member allows the movement ofthe endless chain in the axial direction of the driven sprocket wheel.6. The chain alignment structure for a bicycle transmission according toclaim 1, wherein rollers are arranged in the chain guide member.
 7. Thechain alignment structure for a bicycle transmission according to claim6, wherein the rollers are arranged outside of an annular space that theendless chain defines.
 8. The chain alignment structure for a bicycletransmission according to claim 1, wherein the chain guide memberincludes an upper guide portion arranged above a path of the endlesschain, a lower guide portion arranged below the chain path, and avertical connecting portion that connects the upper guide portion andthe lower guide portion together.
 9. The chain alignment structure for abicycle transmission according to claim 5, wherein a comb portion isformed on the chain guide member, said comb portion having a pluralityof teeth inserted into gaps formed between tips of the plurality ofdriven sprocket wheels, respectively.
 10. A bicycle, comprising: aframe, said frame including a pair of left and right main framesextending from a head pipe rearward and obliquely downward, a down tubeextending from front lower ends of the pair of main frames rearward andobliquely downward, a saddle frame extending rearward from for the pairof mainframes; a saddle, said saddle being supported by the saddleframe; a pair of left and right front forks, said pair of front forksbeing supported by the head pipe and supporting a front wheel; a pair ofleft and right swing arms, said pair of swing arms being supported bythe main frames and supporting a rear wheel; a drive sprocket wheel,said drive sprocket wheel being rotatably driven by a crankshaft; adriven sprocket wheel, said driven sprocket wheel being drivablyconnected with an output shaft which is rotated in an interlockingmanner with a drive wheel of the bicycle; and an endless chain, saidendless chain being wound around the drive sprocket wheel and the drivensprocket wheel, wherein a chain guide member is arranged on anendless-chain-reel-in side of the drive sprocket wheel.
 11. The bicycleaccording to claim 10, wherein the driven sprocket wheel is configuredto be always integrally rotated with the output shaft, and a one-wayclutch which transmits rotation in the normal direction of thecrankshaft to the drive sprocket wheel is arranged between thecrankshaft and the drive sprocket wheel.
 12. The bicycle on according toclaim 10, wherein the chain guide member includes a pair of guideportions which are arranged substantially in parallel with atransmission locus of the chain in a state that the guide portionssandwich the chain, and the pair of guide portions are connected witheach other by way of a connecting portion.
 13. The bicycle according toclaim 10, wherein the driven sprocket wheel and the drive sprocket wheelare covered with a single casing which is fixed to the vicinity of thecrankshaft, and the chain guide member is fixed in the inside of thecasing.
 14. The bicycle according to claim 10, wherein there are aplurality of driven sprocket wheels which differ in diameter and arecoaxially mounted on the output shaft, a winding changeover unit whichchanges over the winding among the plurality of driven sprocket wheelsaround which the endless chain is wound is provided, and the chain guidemember allows the movement of the endless chain in the axial directionof the driven sprocket wheel.
 15. The bicycle according to claim 10,wherein rollers are arranged in the chain guide member.
 16. The bicycleaccording to claim 10, wherein the rollers are arranged outside of anannular space that the endless chain defines.
 17. The bicycle accordingto claim 10, wherein the chain guide member includes an upper guideportion arranged above a path of the endless chain, a lower guideportion arranged below the chain path, and a vertical connecting portionthat connects the upper guide portion and the lower guide portiontogether.
 18. The bicycle according to claim 14, wherein a comb portionis formed on the chain guide member, said comb portion having aplurality of teeth inserted into gaps formed between tips of theplurality of driven sprocket wheels, respectively.